Most people know that electrically active cells in nerves, in the heart and in the brain generate electrical currents, and that somehow these result in measurements we all have heard about, such as the electrocardiogram. But how? That is, what is it that happens within the electrically active tissue that leads to the creation of currents and voltages in their surroundings that reflect the excitation sequences timing, and condition of the underlying tissue. This course explores that topic. Rather than being a primer on how to interpret waveforms of any kind in terms of normality or disease, the goal here is to provide insight into how the mechanism of origin actually works, and to do so with simple examples that are readily pictured with simple sketches and one’s imagination, and then moving forward into comparison with experiments and finding outcomes quantitatively.

À partir de la leçon

Week 7

As a conclusion to the course, two diverse subjects are considered. One, the multipole expansion, is used when one has no model of the true origin of observed potentials but still needs to create an “equivalent” model to represent the data. The other, cardiac excitation, is characterized by large, broad excitation waves. One sees that an equation for the extracellular potentials has the same components as the expression for a simple cylindrical fiber, translated into a geometrically suitable form.